After chairing another meeting of the Cobra emergency committee, David Cameron pledged continuing assistance to those who had suffered the most.

He said: "I want to reassure everyone affected by these terrible storms that we will continue to keep up our urgent response and help get them back on the move."

He said more pumps would be sent to clear roads, and he said army engineers were working with National Rail on options to shore up the section of the key railway line between Devon and Cornwall, which was badly damaged in Wednesday's storms.

Earlier, when asked whether visiting flood-hit Somerset would be more useful than talking in London, Mr Cameron said: "It was because of Cobra that we got extra pumps down to Somerset. It was because of Cobra that I forced through the extra £100m of funding.

"It's because of Cobra that the army is available to help in Somerset. If there's anything that they can do to help, they will do."

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The storm caused huge damage to the railway line in Dawlish, which is expected to take weeks to fix

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Residents of the Somerset Levels have been urged to evacuate as the area braces for more flooding

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Royal Marines are helping reinforce defences in the Somerset Levels with sandbags

Some residents in the Somerset Levels have heeded warnings to evacuate their homes amid fears that flood defences could be overwhelmed, but others have remained, apparently prepared to risk the consequences in order to protect their properties from looters.

Somerset County Council said the marines would support its own teams, reinforcing banks with sand bags and helping people move their belongings.

In other developments:

Some people living on the Somerset Levels have evacuated their homes while a rest centre has been set up in Bridgwater for evacuees there

Communities Secretary Eric Pickles told MPs the government would carry out a "rapid review of the additional work needed to restore our flood defences and maintain them".

The extra £30m - on top of the £100m announced by Mr Cameron on Wednesday - would "cover costs incurred during the current emergency response and recovery, as well as essential repairs to ensure that defences are maintained", said Mr Pickles, who was standing in for Environment Secretary Owen Paterson, who is to have emergency eye surgery.

Analysis

A key railway running right beside a violent sea was always vulnerable, and experts knew the risks. Time after time reports warned that storms, combined with a rising sea, could threaten this vital link.

In fact, three years ago the government staged a photo opportunity at Dawlish to launch its new strategy on preparing critical infrastructure for climate change.

The minister at the time, Lord Henley, declared: "Business as usual is not an option." A senior engineer from Network Rail boasted of being "ahead of the game, with a clear climate resilience strategy".

Studies have modelled the shape of the seabed at Dawlish and assessed the potential impacts. Now engineers face the challenge of coming up with an immediate fix to get the trains running again while working out how to keep the line safe in the future.

But UKIP, which dismissed the extra spending as "far too little, far too late", called on the government to channel part of its foreign aid budget into helping those worst hit by the flooding.

It is urging the government to suspend payments from the £11bn annual budget and divert them "on a month by month basis" to areas in most need of repairs to storm-damaged property, renewal of flood defences and restoration of transport links.

Earlier, Transport Secretary Patrick McLoughlin told MPs he would review alternative rail routes to south-west England after the storm caused massive damage at Dawlish to the main railway between Devon and Cornwall.

Cost of destruction

Robin Gisby, of Network Rail, told BBC Radio 4's Today programme it would take "several weeks" to fix the line, which is regarded as a vital transport link between the region and the rest of the country.

Limited services were running between Plymouth and Penzance, with rail replacement services bridging the gap.

Business leaders in Devon and Cornwall are worried that the destruction of the line will cost the local economy millions of pounds.

At the scene

By Sarah RansomeBBC News

There's not much to smile about on the Somerset Levels at the moment, and as yet more rain swept across the waterlogged landscape, there were grim faces on the farm I visited, when a large red truck came into view.

It was here to take away cattle already moved into sheds. With more storms to come, convoys have been leaving waterlogged villages and hamlets today, taking animals to safe, dry havens.

In the part-evacuated village of Moorland, homeowners who stayed have been collecting extra sandbags to try to hold back any rising water.

As he pulled a trolley stacked high with the grimy grey cargo, one resident tried to joke that there would soon be more sand here than on the beach at Weston-super-Mare. But the shadowy smile could not hide for long the underlying anxiety etched into his face after weeks of worry.

Weather information

BBC weather presenter Peter Gibbs said gusts of up to 70mph were expected during the next round of storms, due to hit the South West on Friday night, with the risk of even stronger gusts on Saturday night.

"There is no sign of an end to this unsettled weather right into next week," he said.

Electricity supplies have been restored to more than 1,700 customers in south-west England, who had been without power.

Despite the problems expected by businesses, the managing director of St Austell Brewery, James Staughton, said of the region: "We are very resilient, we are very open for business and I'm sure we'll find a way round it, but we need a lot of government support to make it happen."